This invention relates to water hardenable orthopaedic splints and supports.
In the formation of casts, it is useful to use a water hardenable material, such as Plaster of Paris or a water hardenable urethane, as disclosed for examples in U.S. Pat. No. 3,373,741 or in German Offenlegenschrift No. 2,651,089.
With regard to the construction of water hardenable casts, plaster of paris casts have been used for many years. They normally involve the use of several layers of cotton xe2x80x9cskrimxe2x80x9d or a very loosely woven cloth using thin threads and having large openings, and these layers of cloth are embedded in plaster of paris. In use, strips of the skrim and plaster of paris are dipped in water and wrapped around the injured portion of the anatomy. Normally padding is employed next to the skin to protect from the hardening cast material. As the plaster of paris hardens, it is somewhat exothermic, but there is no gas released. U.S. Pat. No. 3,043,298 (Brickman, et al.) assigned to Johnson and Johnson, discloses the addition of hydroxypropyl methyl-cellulose (HPMC) to a Plaster of Paris bandage to be used as an orthopaedic cast which gives the Plaster of Paris a creamy and viscous consistency or texture when wet with water just prior to application. More specifically, a plain Plaster of Paris cast without additives has a somewhat granular texture, akin to wet sand, while with the addition of HPMC it is somewhat smoother in texture with a consistency similar to mud or smooth clay.
Concerning water hardenable urethane casts, they are usually formed of a high strength fabric which may be {fraction (1/16)} of an inch or so thick, and which is normally knitted so that there are small visible openings through the fabric. The water hardenable urethane material is impregnated into the fabric. At the time of use, assembly may be dipped in water prior to application to the injured part of the anatomy. Again, padding is usually employed to protect the skin from the cast material. In the case of urethane, the exothermic hardening reaction is accompanied by the release of carbon dioxide, and the wet urethane is very sticky. With the outgassing of the CO2 and the resulting bubbling out of the urethane material, the warm sticky assembly would be difficult for the doctor or orthopaedic technician to handle, and properly apply to the patient. One technique directed to overcoming this problem is disclosed in Mathew T. Scholz, et al. U.S. Pat. No. 4,667,660 and U.S. Pat. No. 4,774,937. As disclosed in these patents, the coefficient of friction of a curable resin sheet may be reduced by using either a lubricant of a certain type bound to the resin, and/or by using additive lubricants which are either (a) polysiloxanes, (b) surfactants, and polymers consisting of hydrophilic groups of certain types. It was the considered view of knowledgeable persons in the orthopaedic field that the techniques as described in the Scholz, et al. patents were the only practical way of obtaining the desired low coefficient of friction where water hardenable urethane materials were employed. Thus, for example, the assignee of the Brickman patent cited above, apparently employed the lubricants of the Scholz, et al. patents for its hardenable urethane cast assemblies, see Minnesota Mining and Manufacturing Co. v. Johnson and Johnson, 24 U.S.P.Q.2d 1321, 976 F.2d 1559 (CAFC 1992).
With regard to aspects of the invention emphasized in U.S. patent application Ser. No. 09/088,905 cited above, it has previously been proposed to use water-hardenable materials in orthopaedic supports and casts; and typical patents disclosing such products include U.S. Pat. No. 4,996,979, granted Mar. 5, 1991, and U.S. Pat. No. 4,683,877, granted Aug. 4, 1987. However, when materials as disclosed in these patents are employed, the flow of liquid through the open cell foam or layers of fabric, as well as the strength of the orthopaedic support may not be subject to the desired level of control.
It is also noted that these prior art products mentioned above have other problems. Thus, for example with regard to the casts or supports using layers of material, care must be taken to firmly engage the layers during the setting period to ensure unitary bonding of the entire layered cast or assembly. Doctors practicing in this area even have a saying: xe2x80x9crub it like you love it,xe2x80x9d to encourage full engagement of the layers during hardening of the water-hardenable material. This step obviously requires care and expertise, as it is undesirable to apply undue force to an injured limb involving broken bones, for example. Further, if this technique is not properly employed, the layers will not fully bond together, and the cast or support will be weak, and the layers could separate. Also with regard to the hardenable splints or supports using open cell foam, they may lack sufficient flexibility and conformability to properly fit the three-dimensional parts of the anatomy requiring splinting or support.
Fiat rigid panels have also been proposed using doubleknit fabrics and hardenable resins, as indicated by U.S. Pat. No. 5,166,480, granted Nov. 24, 1992, and entitled xe2x80x9cKnitted Fabric Panel Structure and Process of Manufacture.xe2x80x9d Attention is also directed to U.S. Pat. No. 5,334,442, granted Aug. 2, 1994. This patent discloses an intermediate pliant sheet which may be made of a single layer fabric such as a fiberglass fabric impregnated with a water-hardenable material. Then, on both sides of this pliant layer, the patentees disclose the use of layers of doubleknit material. Thus, with doubleknit material present in the assembly, it is not used to receive the water-hardenable material but is only used for padding.
As noted above, prior art orthopaedic products have involved shortcomings in the flow control of water to the water-hardenable material and the strength of the orthopaedic device.
It is an important object of the present invention to provide an orthopaedic splint or support which is smooth and is not rough so that it could catch on clothing or the like; and which is also smooth and velvety as it is being applied and molded to the injured member of the patient, while concurrently providing a strong layer-to-layer bonding when overlapping layers of the casting material are used.
In accordance with one specific illustrative embodiment of the invention, the foregoing object is achieved through the use of high strength fabric, preferably doubleknit type material impregnated both with water hardenable urethane and also with HPMC. Without the HPMC, following water immersion, the urethane becomes very sticky and-has an exothermic reaction accompanied by the release of carbon dioxide (CO2) and the result is a bubbly, sticky assembly which is very difficult to work with. However, the addition of the HPMC acts as a controlling agent for the assembly and, in the case of casting tapes, permits easy handling and wrapping of the layers of the casting tape, and facilitates controlled bubbling of the CO2 through the layers of tape, ensuring layer-to-layer bonding of the urethane impregnated layers of tape, to form a high strength cast. Further, the final cast is remarkably smooth and free of the coarse and rough outer surfaces characteristic of synthetic casts made in accordance with the patents cited hereinabove.
In practice, the HPMC is supplied in powder form and contains a small percentage, such as 1%, content of water. Because the hardenable urethane is water sensitive, this would normally be considered to be a negative factor, as the manufacturing process is carefully controlled to eliminate moisture and maintain very low humidity conditions. The HPMC does not dissolve when admixed with the urethane chemistry, but simply becomes encapsulated within the viscous resin. In the course of coating the urethane resin combination onto the supporting fabric, it may be thoroughly mixed to avoid separation as it is coated. Also, because the HPMC stays in powder form, the level or amount of rubbing of the material following water activation controls the physical properties of the cast or splint. More specifically, the tackiness and slipperiness of the assembly is determined by the amount of rubbing as the HPMC becomes somewhat gelatinous when contacted by water. Accordingly, if the doctor or medical technician who is applying the splint or support does not want very slippery material, he would merely not rub the cast or splint very much. The more the assembly is rubbed, the more the HPMC is exposed to water, and the coefficient of friction is further reduced.
It is further noted that as the cast or splint dries, the HPMC loses its slippery nature quickly as compared with silicone/urethane resin combination used in certain prior art products, and the resultant layered splints or casts are stronger and are more resistant to xe2x80x9cpeelxe2x80x9d or the delamination of adjacent bonded layers.
The HPMC allows the HPMC/resin assembly to foam and swell, thereby promoting a creamier texture to the urethane. We therefore have a much smoother cast on the surface. This is desirable because prior art urethane resin casts were very porous and had a rough surface due to the surface of the lightly coated fiberglass fabric becoming hard and abrasive like a metal screen. Because our HPMC reacts with water, we can enjoy a smoother surface by simply allowing the chemistry to become gelatinous, then smoothing the creamy material by simply rubbing the surface of the outer layer. The result is better for the patient. A smoother cast surface means less rubbing against adjacent clothing during the daytime and less rubbing against adjacent skin or a partner""s skin during sleep. Also it is more comfortable for the skin of the fingers which come in contact with the cast throughout the full rehabilitation period using certain cast configurations. For example, in the case of an arm and wrist cast, or thumb spica cast, or an ulnar gutter cast, immobilization near the fingers for four to six weeks at a time, the friction with and possible irritation of adjacent fingers is a significant factor.
Returning to the advantages as compared with prior art water hardenable urethane casts, in those prior art systems the use of silicone or other similar additives, which always retain their slippery qualities, can reduce the strength of the completed cast or splint by reducing inter-laminar strength; and, in addition, an element of control of this level of slipperiness or the coefficient of friction, is lost.
It is also noted that the BPMC has a tendency to initiate foaming in the urethane resin after both are activated by water. Further, it was noted that HPMC has the effect of initiating better lamination of the cast/splint. In fact, it has been noted that it works in combination with the off-gassing which is a natural byproduct of the water-activated resin. Because the HPMC increased the creaminess of the resin after activation by water, it appears to be xe2x80x9ccarriedxe2x80x9d by the off-gassing into adjacent layers resulting in (a) stronger lamination, and (b) less need to rub the cast in order to initiate interlamination bonding. This results in reduced skill requirements for the applicator. HPMC as combined with the urethane resin not only makes the product slippery (when exposed to water), it also promotes foaming and swelling of the chemistry which mechanically initiates a flowing of the resin from one layer into another aided by the off-gassing of the reacting resin. It is understood that the bursting bubbles have a tendency to xe2x80x9cmovexe2x80x9d the resin into the holes and structure of the adjacent fabric layers, increasing laminate bonding.
Accordingly, a broad aspect of the invention involves the use of HPMC and a water hardenable resin applied to a fabric to provide an improved high strength casting or splinting material which may be used in tape form with improved lmaination strength, or in blanks for single layer usage.
In one preferred embodiment, the HPMC may be applied to the surface of the resin, while in other embodiments it may be mixed into the resin, for example, in powdered form.
The following paragraphs relate to aspects of the invention included in Ser. No. 09/088,905, cited hereinabove.
Accordingly, a principal object of the present invention is to improve both the control of the flow of water to the curable resin in orthopaedic supports or splints, and concurrently to provide the desired strength for the product.
Additional objects include increasing the reliability and simplifying the application, increasing conformity, reducing the thickness and weight while increasing the strength of casting materials.
In accordance with a method for forming an orthopaedic support illustrating the principles of the invention, an integral double layer fabric with a central open-work matrix, such as a doubleknit material, is employed to form a water hardenable splint or cast. The central open-work matrix includes integrally fabricated filaments or yarns which extend back and forth between the upper and lower fabric layers. This doubleknit type material is impregnated with a water-hardenable material under low humidity conditions, and is packaged in a water-vapor impermeable package. The impregnated doubleknit type material is located adjacent the injured portion of the anatomy, such as a broken bone, so that the material conforms to the desired configuration of the injured part of the anatomy. Water is applied through the open-work matrix of the doubleknit material to rapidly wet the water-hardenable material, to cause stiffening of the orthopaedic support and preventing undesired movement of the injured part. Water is applied to the doubleknit type material prior to application to the anatomy in the case of tapes and flat splinting shapes; and in the case of soft goods type products, following application of the soft goods support to the anatomy.
The orthopaedic support preferably includes high strength material such as glass fiber fabric, keviar fibers, aramids, or other high strength fibers, to provide strength to complement the rigidity or stiffness of the water-hardenable material.
The orthopaedic support using the doubleknit type fabric with its open-work central matrix may take a number of forms, including a tape, a flat or contoured splint shape configured to fit an injured portion of the anatomy, or a soft goods product having straps to secure the support in place, and having the doubleknit fabric within its construction.
Regarding the soft goods type support, it may be similar to that showing in U.S. Pat. No. 4,996,979, and may include either a single layer of impregnated doubleknit type fabric, or a plurality of such layers, with one or more intermediate water distribution networks. In addition, the soft goods support may include one or more of the following additional features: (1) an outer semi-flexible or semi-rigid member of plastic or the like to provide a general shape to the assembly prior to hardening of the material; (2) water impermeable layers for confining the water; (3) soft cloth lining material for engaging the skin of the injured party; and (4) straps for holding the assembly onto the injured part of the anatomy.
Incidentally, regarding water-hardenable materials and other matters, the disclosure of U.S. Pat. No. 4,996,979 is hereby incorporated into this specification by reference.
It is further noted that hardenable casts and splints formed of appropriate doubleknit type material have higher strength than the prior art foam or multi-layer hardenable splints.
Concerning the coefficient of friction of the various casting materials as discussed above, the following experiment was conducted, in accordance with ASTM Standard Test Method Designation D-1894-95. In the tests, samples of the various casting materials were immersed in water. Fifteen to eighteen seconds subsequent to removal, a stainless steel sled is gently placed on each sample and is then pulled across the sample. The coefficient of friction equals the force required to pull the sled divided by the weight of the sled.
Employing these test conditions and taking several readings during each test, the kinetic coefficient of friction of a commercial embodiment of a product as disclosed in the Scholz patent was about 0.31; and the coefficient of friction of one illustrative embodiment of the present invention, including the doubleknit material, water hardenable urethane and the HPMC, was approximately 1.76.
Furthermore, measurements of the surface roughness or deviation from flatness were also taken for the various cast materials. The surface roughness or deviation from flatness is the estimated depth of recesses of irregularities from a straight line or a flat plane in areas where the cast or splint is substantially flat. The surface roughness or deviation from flatness of the plaster of paris cast as disclosed in Brickman was approximately 0.015 to 0.025 inch; the surface roughness of a Scholz cast was about 0.035 inch; and the surface roughness of one illustrative embodiment of the present invention was generally less than 0.010 inch.